Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $89.86   8.134%   $97.1692   $97.17   $97.15   $97.20  
  Purchase #2 $171.25   13.853%   $194.9733   $194.97   $194.95   $195.00  
  Purchase #3 $244.28   4.578%   $255.4631   $255.46   $255.45   $255.50  
  Purchase #4 $139.97   12.425%   $157.3613   $157.36   $157.35   $157.40  
  Purchase #5 $179.59   8.592%   $195.0204   $195.02   $195.00   $195.00  
  Purchase #6 $46.36   6.154%   $49.213   $49.21   $49.20   $49.20  
  Purchase #7 $93.88   12.397%   $105.5183   $105.52   $105.50   $105.50  
  7 purchase totals = $965.19       $1,054.7186   $1,054.71   $1,054.60   $1,054.80